1. Field of the Invention
This invention relates to an image processing apparatus for embedding another information into image information without causing the unnatural sense of vision by use of a redundancy included in the image information, and/or an image processing apparatus for extracting another information from the image information into which the another information is embedded.
2. Description of the Related Art
The technique for superposing text data on an color image and recording the same is disclosed in the article by Nakamura, Matsui et al. "Combining/Coding Method of Text Data to Image by Color Density Pattern" Image Electronics Institution Papers, Vol. 17, No. 4 (1988), pp. 194-198. According to this technique, an attention is directed to the point that image data has a higher redundancy. Another data, for example, text data is superposed on the redundancy portion of the image data by use of color density pattern method. However, in general, the resolution is lowered when the color density pattern method is used and it becomes impossible to display a high-definition image. Further, the image quality is degraded by irregular color or the like due to a variation in the pixel arrangement caused by superposition of information.
As an example of application of dither image recording capable of permitting higher definition display compared with that of the color density pattern method, the technique is disclosed in the article by Tanaka, Nakamura, Matsui "Embedding of Character Information into Compositional Dither Image by 2k-Dimensional Vector" Image Electronics Institution Papers, Vol. 19, No. 5 (1990), pp 337-343. The technique has a defect that the image quality is degraded when character information is embedded. Further, the technique has another defect that it cannot be applied to the high-definition recording technique such as the error diffusion recording method.
In addition, according to the above techniques, even if it is possible in principle to extract character information or the like from an actually printed image, dither pattern information cannot be precisely printed on paper or the like in the actual general recording process and it is difficult to read such information. Therefore, it becomes extremely difficult to read the embedded information. It is only possible to extract from the image data (such as transmission data and data in the floppy disk) used as a basis for printing. In order to read out coded specified information such as character information from the actual recording image based on the above techniques, it is definitely necessary to use an extremely high precision printer which can print the image with high resolution exceeding the limit of eyesight of a man and reads the image by use of a high precision reading device.
Further, with the above method, noises at the time of recording and reading will occur and it becomes difficult to read the coded information such as character information separately from the image information. In addition, even if the color-recorded image information is recorded by use of a high precision recording device, image dots of respective colors of the color-recorded image information overlap each other, and therefore, it is difficult to form a precise pixel shape. In this case, it is extremely difficult to read pixel data of the respective colors separately from the image information.
Further, in Japanese Patent Disclosure (KOKAI) No. 4-294682, the technique for attaching another information to the yellow ink is described. According to this technique, there occurs no problem when an original image is constructed only by pixels containing only the yellow component. However, when it contains another color, it is impossible to ensure that an image which is not visually significant can be recorded simply by adding yellow. Further, in the case of cyan or magenta which does not contain the yellow component, a problem that the specified information cannot be added occurs.